Composite separator and electrochemical device comprising same

Abstract

The invention relates to a composite diaphragm. The composite diaphragm comprises a porous base material; and a ceramic layer formed on one surface or both surfaces of the porous substrate and containing inorganic particles and a binder, in which the binder contains polyacrylamide and carboxymethyl cellulose having a weight average molecular weight of 180000 g / mol or more and a degree of substitution of 0.6 to 1.2 in a weight ratio of 60 to 90: 40 to 10, the composite diaphragm can simultaneously satisfy excellent mechanical stability, thermal stability and ionic conduction characteristics.

Description

Technical Field

[0001] The present invention relates to a diaphragm and an electrochemical device including the diaphragm. Background Technology

[0002] In recent years, with the increasing capacity and power of electrochemical devices, the requirements for ensuring heat resistance and safety have become increasingly stringent. In particular, the performance requirements of the diaphragm, which plays a very important role, have also become increasingly demanding.

[0003] For example, as a solution to ensure the heat resistance and safety of the diaphragm, composite diaphragms, which incorporate coatings containing inorganic particles such as alumina (Al2O3), silica (SiO2), and zirconium oxide (ZrO2) and binders on a porous substrate, are becoming an important technology. However, in recent years, research has been focused on thin-film diaphragms to achieve high capacity and high power characteristics in electrochemical devices. The binders used in existing composite diaphragms have insufficient adhesion to both the substrate and the inorganic particles, resulting in reduced mechanical strength and / or heat resistance as the inorganic particle coating becomes thinner.

[0004] Research is ongoing to address this issue, but in the case of adhesive materials with improved heat resistance, the adhesive strength is insufficient, or when attempting to improve the adhesive strength of the diaphragm, there are limitations such as deterioration of properties like air permeability and interfacial resistance, leading to reduced device performance.

[0005] [Existing Technical Documents]

[0006] [Patent Literature]

[0007] Korean Patent Publication No. 10-2015-0071453A Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] One embodiment of the present invention relates to a composite membrane comprising: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, wherein inorganic particles are connected and fixed by an adhesive to form pores between the inorganic particles, and a composite membrane is provided in which the inorganic particles of the ceramic layer and a specific adhesive are used simultaneously, thereby simultaneously possessing excellent heat resistance and adhesion.

[0010] Another embodiment of the present invention provides an electrochemical device that uses the composite separator, thereby exhibiting excellent battery performance and safety.

[0011] (II) Technical Solution

[0012] One embodiment of the present invention provides a composite membrane comprising: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, wherein the ceramic layer comprises inorganic particles and a binder, wherein the binder comprises polyacrylamide in a weight ratio of 60 to 90:40 to 10 and carboxymethyl cellulose having a weight-average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.2.

[0013] The weight-average molecular weight of the carboxymethyl cellulose can be from 180,000 g / mol to 1,500,000 g / mol.

[0014] The degree of substitution of the carboxymethyl cellulose can be from 0.7 to 1.0.

[0015] The weight-average molecular weight of the polyacrylamide can be from 150,000 g / mol to 250,000 g / mol.

[0016] In the composite membrane according to one embodiment, the content of the binder may be from 0.1 parts by weight to 10 parts by weight relative to 100 parts by weight of the inorganic particles.

[0017] The average particle size of the inorganic particles can be from 0.1 μm to 1.0 μm.

[0018] The inorganic particles may be selected from one or more of boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3 and SiC.

[0019] The porous substrate may be hydrophilic surface treated.

[0020] The total thickness of the ceramic layer can be from 0.5 μm to 10 μm.

[0021] According to one embodiment, the composite diaphragm, after being placed at 150°C for 60 minutes, exhibits a thermal shrinkage rate of less than 4% in both the mechanical direction (MD) and transverse direction (TD).

[0022] In the composite diaphragm according to one embodiment, when evaluating the degree of foreign matter adhesion to the paperboard surface after paperboard testing, the area occupied by the adhered foreign matter relative to the paperboard area can be less than 5%.

[0023] [Cardboard Test]

[0024] (A black cardboard and a rubber pad measuring 2cm × 10cm were placed sequentially on the ceramic layer of a composite diaphragm sample measuring 5cm × 10cm. While applying a force of 10N to the rubber pad using a pressing device, the cardboard was pulled horizontally out by 60mm at a speed of 0.1m / s to test the degree to which foreign matter adhered to the surface of the cardboard.)

[0025] Another embodiment of the present invention provides a method for manufacturing a composite membrane. The method for manufacturing a composite membrane according to one embodiment may include the step of coating a ceramic layer forming composition comprising an adhesive and inorganic particles onto one or both sides of a porous substrate and drying it to form a ceramic layer, wherein the adhesive may comprise polyacrylamide in a weight ratio of 60 to 90:40 to 10 and carboxymethyl cellulose having a weight average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.2.

[0026] Another embodiment of the present invention provides an electrochemical device, which according to one embodiment may include a positive electrode, a negative electrode and a composite membrane, wherein the composite membrane may include: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, and the ceramic layer comprises inorganic particles and a binder, the binder may comprise polyacrylamide in a weight ratio of 60 to 90:40 to 10 and carboxymethyl cellulose having a weight average molecular weight of more than 180,000 g / mol and a degree of substitution of 0.6 to 1.2.

[0027] (III) Beneficial Effects

[0028] The composite membrane according to one embodiment can simultaneously satisfy excellent mechanical stability, thermal stability, and ionic conductivity. Specifically, the composite membrane according to one embodiment includes a porous substrate and a ceramic layer, in which inorganic particles are connected and fixed by an adhesive, thereby forming pores between the inorganic particles. Due to the excellent adhesion between the inorganic particles and between the inorganic particles and the substrate, the shedding of inorganic particles and shrinkage at high temperatures can be effectively suppressed.

[0029] Furthermore, in the composite membrane according to one embodiment, even if the thickness of the formed ceramic layer is very thin, it can achieve superior adhesion and heat resistance compared to existing ceramic layers with the same thickness, and the electrochemical device using the composite membrane can simultaneously meet the requirements of safety, high capacity and high power characteristics. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view showing a composite diaphragm according to one embodiment. Detailed Implementation

[0031] In this specification, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

[0032] Unless otherwise specified in the context, the singular form used in this specification may include the plural form.

[0033] Throughout this specification, unless otherwise specifically stated to the contrary, "comprising / including," "having," "containing," or "having" a constituent element means that it may also include other constituent elements, rather than excluding other constituent elements, and does not exclude elements, materials, or processes not further listed.

[0034] The numerical ranges used in this specification include lower and upper limits, all values ​​within that range, increments logically derived from the form and width of the defined range, all values ​​defined therein, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specifically defined, values ​​outside the defined numerical range that may occur due to experimental error or rounding are also included within the defined numerical range.

[0035] In this specification, unless otherwise specifically defined, “about” can be considered as a value within 30%, 25%, 20%, 15%, 10% or 5% of the explicitly stated value.

[0036] In this specification, "average particle size" refers to "D50," which is the particle size of inorganic particles corresponding to a cumulative fraction of 50% based on volume. The average particle size can be obtained by collecting samples of the inorganic particles being measured according to ISO 13320-1 standard and analyzing the particle size distribution using a Microtrac S3500. Furthermore, "D90" refers to the particle size corresponding to a cumulative fraction of 90% based on volume, and "D10" refers to the particle size of inorganic particles corresponding to a cumulative fraction of 10% based on volume. D90 and D10 can be obtained using the same method as D50.

[0037] In this specification, carboxymethyl cellulose (CMC) refers to cellulose in which the hydroxyl groups (-OH) are surrounded by -OCH2COOH and / or -OCH2COO. - M + The substituted and etherified cellulose derivative, wherein the M +It is an alkali metal cation, and can be selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), etc. In this specification, the "degree of substitution (DS)" of carboxymethyl cellulose refers to the average number of the aforementioned substituents contained in one dehydrated glucose unit of the cellulose molecule, which can be measured by known or commonly used methods, for example, according to ASTM D1439, or by... 1 H-NMR or 13 Calculations were performed using C-NMR analysis.

[0038] The degree of substitution (DS) of carboxymethyl cellulose (CMC) was measured using a titration method according to ASTM D1439. The experiment used a magnetic stirrer, aspirator, dry oven, 300 mL beakers, pipettes, 250 mL Erlenmeyer flasks, and Petri dishes. The reagents used were 80% ethanol, 100% ethanol, 0.1 N sodium hydroxide (NaOH) solution, phenolphthalein indicator, and 0.1 N sulfuric acid (H₂SO₄) solution.

[0039] Specifically, add 150 mL of 80% ethanol to a 300 mL beaker, followed by 10 mL of 1N nitric acid (HNO3). Add approximately 1 g to 2 g of CMC sample and stir for 1 hour to form CMC acid. Afterward, let stand for approximately 10 to 20 minutes, then remove (decant) the supernatant.

[0040] Next, add another 150 mL of 80% ethanol, stir for 30 to 40 minutes, and then remove the supernatant again. For the precipitated CMC acid, filter using a suction filter, wash with 500 mL of 80% ethanol, and then wash again with 100% ethanol once or twice.

[0041] Take the middle fraction of the purified CMC acid and transfer it to a clean weighing dish. Dry it in a drying oven for 20 to 30 minutes. After drying, accurately weigh approximately 0.2 ± 0.05 g of the sample and add 25 mL of 0.1 N NaOH solution. Transfer the sample solution to a 250 mL Erlenmeyer flask and add 100 mL of distilled water. Stir for 40 to 60 minutes until completely dissolved.

[0042] Then, add 2 to 3 drops of phenolphthalein indicator and titrate with 0.1N H2SO4 solution while stirring continuously until the solution color changes from red to colorless.

[0043] The number of millimoles (A) of CMC acid in 1g of dried sample is calculated using the following formula.

[0044]

[0045] Then, the degree of substitution (DS) is calculated from A using the following formula.

[0046]

[0047] The present invention will now be described in detail. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described herein.

[0048] This invention provides a composite membrane that can simultaneously ensure excellent mechanical stability, thermal stability, and ionic conductivity.

[0049] Specifically, a composite membrane according to one embodiment may include: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, wherein the ceramic layer comprises inorganic particles and a binder, wherein the binder may comprise polyacrylamide in a weight ratio of 60 to 90:40 to 10 and carboxymethyl cellulose having a weight-average molecular weight of more than 180,000 g / mol and a degree of substitution of 0.6 to 1.2.

[0050] In the composite membrane according to one embodiment, by applying an adhesive made of carboxymethyl cellulose and polyacrylamide mixed in a specific ratio, satisfying the weight-average molecular weight and degree of substitution combination as described above, excellent adhesion between inorganic particles and between inorganic particles and the substrate can be achieved, and excellent heat resistance can be obtained. Furthermore, in the composite membrane according to one embodiment, even if the thickness of the formed ceramic layer is very thin, excellent adhesion and heat resistance can be achieved, and the electrochemical device using the composite membrane can simultaneously meet the requirements of safety, high capacity, and high power characteristics.

[0051] In one embodiment, the weight-average molecular weight of the carboxymethyl cellulose can be above 180,000 g / mol, above 190,000 g / mol, or above 200,000 g / mol, and can be below 2,000,000 g / mol, below 1,800,000 g / mol, below 1,500,000 g / mol, below 1,300,000 g / mol, or below 1,000,000 g / mol. Specifically, it can be between 180,000 g / mol and 2,000,000 g / mol, between 180,000 g / mol and 1,500,000 g / mol, between 180,000 g / mol and 1,300,000 g / mol, or between 200,000 g / mol and 1,000,000 g / mol, and can include all possible combinations of the upper and lower limits of the above numerical ranges. The weight-average molecular weight can refer to the weight-average molecular weight calculated based on a molecular weight calibration curve using a polysaccharide standard sample measured by GPC methods. A sample was obtained by dissolving carboxymethyl cellulose in a standard at approximately 0.1% w / v, and the sample was injected into a GPC instrument for measurement.

[0052] Furthermore, the degree of substitution of the carboxymethyl cellulose can be 0.6 to 1.2, 0.6 to 1.1, 0.6 to 1.0, 0.7 to 1.2, 0.7 to 1.1, 0.7 to 1.0, 0.8 to 1.2, 0.8 to 1.1, 0.8 to 1.0, 0.9 to 1.2, 0.9 to 1.1, or 0.9 to 1.0, and can include all possible combinations of the upper and lower limits of the above numerical ranges. By using carboxymethyl cellulose that satisfies the above-mentioned combinations of weight-average molecular weight and degree of substitution, excellent coatability is achieved when the ceramic layer is coated onto the surface of a porous substrate using a coating slurry during the formation of the ceramic layer. Furthermore, in the composite membrane containing the carboxymethyl cellulose, even with a thin ceramic layer, the effects of simultaneously improving heat resistance and adhesion can be further enhanced, for example, by improving heat resistance and the adhesion between inorganic particles or between the ceramic layer and the porous substrate.

[0053] In one embodiment, the polyacrylamide (PAAm) may be a homopolymer containing 100 mol% of acrylamide polymer units. When the polyacrylamide is a copolymer further comprising polymer units derived from monomers other than acrylamide (e.g., copolymer units selected from vinyl alcohol, acrylonitrile, acrylic acid, etc.), it may undergo side reactions with the positive electrode, negative electrode, and electrolyte, potentially reducing battery performance. Therefore, a polyacrylamide homopolymer is most preferred, but the content of copolymer units tolerable for performance degradation is acceptable; for example, the amount of copolymer units used may be limited to 5 mol% or less, 3 mol% or less, 1 mol% or less, 0.5 mol% or less, or 0.1 mol% or less.

[0054] The weight-average molecular weight of the polyacrylamide can be above 100,000 g / mol, above 150,000 g / mol, above 180,000 g / mol, or above 200,000 g / mol, and can be below 500,000 g / mol, below 400,000 g / mol, below 300,000 g / mol, or below 250,000 g / mol. Specifically, it can be from 100,000 g / mol to 300,000 g / mol or from 150,000 g / mol to 250,000 g / mol, or it can include all possible combinations of the upper and lower limits of the above numerical ranges, but is not limited thereto. The weight-average molecular weight can refer to the weight-average molecular weight calculated based on the molecular weight calibration curve of a polystyrene standard sample measured by GPC method.

[0055] In one embodiment, the inorganic particles can be used without restriction as long as they are of the types commonly used in this art. As a non-limiting example, the inorganic particles can be one or more selected from metal oxides, metal hydrates, metal carbides, metal nitrides, and metal carbonitrides such as boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0056] In one embodiment, the average particle size (D50) of the inorganic particles may be, for example, 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, or 0.1 μm or more, and may be from 0.01 μm to 10 μm, 0.02 μm to 5.0 μm, 0.1 μm to 3.0 μm, 0.1 μm to 2.0 μm, 0.1 μm to 1.0 μm, or 0.1 μm to 0.5 μm, or may include all possible combinations of the upper and lower limits of the above numerical ranges, but is not limited thereto.

[0057] In one embodiment, the content of inorganic particles in the ceramic layer may be 90% to 99.9% by weight, 92% to 99.5% by weight, or 92% to 99% by weight relative to the total weight of the ceramic layer. This content of inorganic particles can be higher than that of conventional coatings that include binders and are formed by the bonding of inorganic particles. Nevertheless, due to its excellent heat resistance and numerical stability, a coating (ceramic layer) with a thinner thickness can be formed.

[0058] In one embodiment, the content of the binder used in the ceramic layer, relative to 100 parts by weight of the inorganic particles, can be less than 10 parts by weight, less than 8 parts by weight, less than 5 parts by weight, less than 3 parts by weight, less than 2 parts by weight, or less than 1 part by weight, and can be more than 0.1 parts by weight, more than 0.5 parts by weight, more than 1 part by weight, or more than 2 parts by weight. Specifically, it can be between 0.1 parts by weight and 5 parts by weight, between 1 parts by weight and 5 parts by weight, between 1 parts by weight and 3 parts by weight, or between these ranges.

[0059] In one embodiment, the mechanical (MD) and transverse (TD) thermal shrinkage rates measured after placing the composite diaphragm at 150°C for 60 minutes can both be below 5%, specifically below 3%, below 2.5%, or below 2.0%.

[0060] Furthermore, in one embodiment, when evaluating the degree of foreign matter adhesion to the paperboard surface after conducting a paperboard test on the composite diaphragm, the proportion of the area occupied by the adhered foreign matter relative to the area of ​​the paperboard can be less than 5%, specifically, it can be less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%.

[0061] The paperboard test method is as follows: A black paperboard measuring 2cm × 10cm and a rubber pad are placed sequentially on the ceramic layer of a composite diaphragm sample measuring 5cm × 10cm. While applying a force of 10N to the rubber pad using a pressing device, the paperboard is pulled horizontally out by 60mm at a speed of 0.1m / s. The degree of foreign matter adhesion to the paperboard surface is tested by evaluating the area. The foreign matter can be a component of the ceramic layer, such as inorganic particles, adhesives, or a combination thereof.

[0062] When evaluating adhesive strength using the paperboard testing method described above, not only the adhesive strength between the substrate and the ceramic layer interface can be considered, but also the adhesive strength between inorganic particles within the ceramic layer. Furthermore, the adhesive strength test results can predict the degree of thermal shrinkage more accurately than existing peel tests. Specifically, when the area occupied by adhered foreign matter calculated through the paperboard test is less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%, it indicates excellent adhesive strength between inorganic particles and between inorganic particles and the substrate, and effectively suppresses thermal shrinkage.

[0063] As an example, existing methods such as peel tests for evaluating the adhesion of inorganic particle coatings in composite diaphragms evaluate the adhesion between the substrate and the inorganic particle coating interface. Therefore, it is difficult to predict the adhesion between inorganic particles, and there is a drawback that the thermal shrinkage characteristics of the diaphragm cannot be accurately predicted through the evaluation value.

[0064] In one embodiment, the porous substrate is not limited to any porous substrate commonly used in this art; for example, the porous substrate can be woven fabric, nonwoven fabric, or porous membrane. Specifically, the porous substrate can be polyethylene, polypropylene, or other polyolefins; polyethylene terephthalate, polybutylene terephthalate, or other polyesters; polyacetal; polyamide; polyimide; polycarbonate; polyetheretherketone; polyaryletherketone; polyetherimide; polyamideimide; polybenzimidazole; polyethersulfone; polyphenylene ether; cyclic olefin copolymers; polyphenylene sulfide; polyethylene naphthalate; glass fiber; Teflon; and / or polytetrafluoroethylene, and any two or more of these can also be used. In the porous substrate, the porous membrane is prepared by dry and wet methods, which are well known in this art and will not be described further.

[0065] In one embodiment, the porosity of the porous substrate may be 20% to 60%, 30% to 60%, 30% to 50%, or 35% to 45%, but is not limited thereto.

[0066] In one embodiment, the porous substrate may be a substrate incorporating polar functional groups by performing a hydrophilic surface treatment, such as carboxyl, aldehyde, hydroxyl, etc. As an example, the hydrophilic surface treatment may be corona discharge treatment or plasma discharge treatment, but there are no particular limitations.

[0067] In one embodiment, the thickness of the porous substrate is not particularly limited. For example, the thickness of the porous substrate can be 1 μm to 100 μm, 1 μm to 50 μm, 1 μm to 30 μm, 5 μm to 20 μm, or any value between the above values.

[0068] In one embodiment, the ceramic layer can be coated on one or both sides of a porous substrate. When the ceramic layer is coated on both sides of the porous substrate, the thicknesses of the ceramic layer coated on one side and the other side can be the same or different. Although not particularly limited, the total thickness of the ceramic layer according to one embodiment can be, for example, 0.1 μm to 10.0 μm, 0.5 μm to 10.0 μm, 1 μm to 10 μm, 1 μm to 8 μm, 1 μm to 5 μm, about 1.5 μm to 5 μm, 2 μm to 5 μm, or 2 μm to 4 μm, and can be values ​​between the above values. In the composite membrane according to one embodiment, excellent adhesion and heat resistance can be achieved even when the thickness of the formed ceramic layer is very thin, so the electrochemical device using the composite membrane can simultaneously meet the requirements of safety, high capacity, and high power characteristics.

[0069] Another embodiment of the present invention provides a method for manufacturing the composite membrane, the method comprising the steps of coating a ceramic layer forming composition comprising an adhesive and inorganic particles onto at least one side of a porous substrate and drying to form a ceramic layer, wherein the adhesive may comprise carboxymethyl cellulose and polyacrylamide having a weight average molecular weight of more than 180,000 g / mol and a degree of substitution of 0.6 to 1.2 in a weight ratio of 10 to 40:90 to 60.

[0070] The porous substrate, adhesive, and inorganic particles are described above, therefore detailed descriptions are omitted.

[0071] The ceramic layer forming composition can be prepared by dispersing binder and inorganic particles, and the aggregated inorganic particles can be dispersed using a ball mill.

[0072] The ceramic layer forming composition may also contain a solvent, which may be water, ethanol, methanol, propanol and other lower alcohols, dimethylformamide, acetone, tetrahydrofuran, diethyl ether, dichloromethane, N-methyl-2-pyrrolidone, hexane, cyclohexane and other solvents or mixtures thereof, but is not necessarily limited to these.

[0073] In one embodiment, the solid content of the ceramic layer forming composition is not particularly limited, but for example, the solid content of the ceramic layer forming composition can be from 1% to 50% by weight, 5% to 30% by weight, or 10% to 30% by weight, but is not limited thereto. Furthermore, the viscosity of the ceramic layer forming composition based on a solid content of 25% by weight can be from 800 mPa·s to 5000 mPa·s, 800 mPa·s to 4000 mPa·s, 800 mPa·s to 3000 mPa·s, or 1000 mPa·s to 3000 mPa·s. Within these ranges, the ceramic layer can be formed more easily, and the heat resistance and adhesion of the diaphragm can be further improved.

[0074] In one embodiment, there are no particular limitations on the method of coating or applying the ceramic layer forming composition onto the porous substrate, but for example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating or inkjet printing can be used.

[0075] In one embodiment, the drying can be carried out by methods such as drying with warm air, hot air, low-humidity air, vacuum drying, far-infrared radiation, or electron beam irradiation. The drying temperature is not particularly limited and can therefore be appropriately adjusted according to the experimental environment or purpose; for example, the drying temperature can be 30°C to 120°C, 30°C to 100°C, 50°C to 80°C, or 50°C to 70°C. The drying time is not particularly limited, but can be 30 seconds to 300 seconds, 60 seconds to 300 seconds, 100 seconds to 300 seconds, 150 seconds to 250 seconds, or approximately 180 seconds.

[0076] Another embodiment of the present invention provides an electrochemical device comprising a composite separator according to one embodiment above. As an example, the electrochemical device may be a lithium secondary battery.

[0077] Specifically, an electrochemical device according to one embodiment may include a positive electrode, a negative electrode, and a composite membrane, wherein the composite membrane may include: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, and the ceramic layer comprising inorganic particles and a binder, the binder comprising carboxymethyl cellulose and polyacrylamide having a weight average molecular weight of more than 180,000 g / mol and a degree of substitution of 0.6 to 1.2 in a weight ratio of 10 to 40:90 to 60.

[0078] The following describes an electrochemical device according to one embodiment, using a lithium secondary battery as an example. However, in addition to including the composite separator according to one embodiment, conventional manufacturing methods and materials in this art can be used to manufacture structures known in this art.

[0079] As an example, the lithium secondary battery can be manufactured using conventional methods, which involve assembling a negative electrode, a separator, and a positive electrode, and then injecting an electrolyte.

[0080] [positive electrode]

[0081] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer located on at least one side of the positive electrode current collector. The positive electrode can be manufactured by coating a positive electrode material slurry onto one or both sides of the positive electrode current collector and then drying and calendering to form the positive electrode mixture layer. The positive electrode material slurry may contain a positive electrode active material and a binder, and may further contain conductive materials, thickeners, etc. as needed.

[0082] The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof, and may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector may be, for example, from 10 μm to 50 μm, but is not limited thereto.

[0083] The positive electrode active material can be used without limitation as long as it is a compound that can reversibly insert and deintercalate lithium ions and is a positive electrode active material commonly used in this technical field. As a non-limiting example, the positive electrode active material can be a composite oxide of lithium with metals selected from cobalt (Co), manganese (Mn), nickel (Ni), iron (Fe), niobium (Nb), magnesium (Mg), copper (Cu), zinc (Zn), molybdenum (Mo), tantalum (Ta), tungsten (W), aluminum (Al) and combinations thereof.

[0084] In one embodiment, the positive electrode active material may be a lithium-nickel composite oxide, which may further contain one or more of cobalt, manganese and aluminum.

[0085] In one embodiment, the positive electrode active material may comprise a nickel-cobalt-manganese (NCM)-based lithium composite oxide. The composition of the metal is not particularly limited, but a high-capacity (high-Ni) composition with a high nickel content may be used. The Ni content in the NCM-based lithium composite oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95. As an example, the NCM-based lithium composite oxide may be LiNi. 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.4 Co 0.2 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc., but not limited to these.

[0086] In one embodiment, the positive electrode active material may be, for example, lithium cobalt oxide-based material, lithium manganese oxide-based material, lithium nickel oxide-based material, lithium iron phosphate-based (LFP, e.g., LiFePO4) material, lithium manganese phosphate-based (e.g., LiMnPO4) material, lithium cobalt phosphate-based (e.g., LiCoPO4) material, lithium iron pyrophosphate-based (e.g., Li2FeP2O7) material, etc.

[0087] The positive electrode adhesive is not particularly limited as long as it is a positive electrode adhesive commonly used in this technical field. The positive electrode adhesive may include non-aqueous adhesives and / or water-based adhesives, or it may include rubber-based adhesives and / or fluorine-based adhesives. For example, it may be one or more of the following: acrylic polymers such as polyacrylate, polymethacrylate, polybutyl acrylate, and polyacrylonitrile; fluorine polymers such as polyvinylidene fluoride, polyhexafluoropropylene, poly(vinylidene fluoride-hexafluoropropylene), and poly(vinylidene fluoride-trichloroethylene); polyvinyl acetate; polyethylene oxide; cellulose; modified cellulose; polyamide; polyacrylamide; rubber; elastomers; etc., but is not limited thereto.

[0088] The conductive material can be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode mixture layer. For example, the conductive material can be a linear conductive material and / or a point-type conductive material. For instance, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, and carbon nanofibers, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, but is not limited thereto. The term "point-type conductive material" as used in this specification can refer to a conventional spherical or particulate conductive material.

[0089] [negative electrode]

[0090] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer located on at least one side of the negative electrode current collector. The negative electrode can be manufactured by coating a negative electrode material slurry onto one or both sides of the negative electrode current collector and then drying and calendering to form the negative electrode mixture layer. The negative electrode material slurry may contain a negative electrode active material and a binder, and may further contain conductive materials, thickeners, etc. as needed.

[0091] The negative electrode current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, etc. The thickness of the negative electrode current collector may be, for example, from 10 μm to 50 μm, but is not limited thereto.

[0092] The negative electrode active material can be used without restriction as long as it is a material that can adsorb and desorb lithium ions and is a negative electrode active material commonly used in this technical field. As a non-limiting example, the negative electrode active material can be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials or tin (Sn)-containing materials, etc.

[0093] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0094] Elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0095] The silicon-containing material can provide further increased capacity characteristics. The silicon-containing material can include Si, SiO x (0 < x ≤ 2), metal-doped SiO x (0 < x ≤ 2), silicon-carbon composites, etc. The metal can include lithium and / or magnesium. Metal-doped SiO x (0 < x ≤ 2) can include metal silicates. The binder, conductive material, and thickener of the negative electrode can use the above-mentioned materials that can be used in manufacturing the positive electrode.

[0096] The negative electrode binder is not particularly limited as long as it is a negative electrode binder commonly used in the art. The negative electrode binder can use rubber-based binders such as styrene-butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC), polyacrylic acid, poly(3,4-ethylenedioxythiophene) (PEDOT)-based binders, etc.

[0097] [Electrolyte]

[0098] In one embodiment, the electrolyte can be a non-aqueous electrolyte, and the non-aqueous electrolyte can contain a lithium salt as an electrolyte and an organic solvent.

[0099] The lithium salt can be represented, for example, by Li + X - As the anion (X - ) of the lithium salt, examples can include F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH- (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0100] The organic solvent may comprise an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive in the battery. The organic solvent may comprise at least one of, for example, carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents. The organic solvent may be selected from, for example, propylene carbonate, ethylene carbonate, butenyl carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, ethyl fluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethanol, isopropanol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc., one or more of these.

[0101] The specific implementation schemes described above will be explained in more detail below through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the claims.

[0102] The physical properties of the following measurement examples are described.

[0103] 1) Viscosity

[0104] The kinematic viscosity of the ceramic layer forming composition (25% by weight solids) was measured using a rotational rheometer (TA Discovery HR-20) and a 60mm diameter flat plate rotor (TA HA Aluminum, 60mm plate) at 25°C and a shear rate of 1 (1 / s). This kinematic viscosity value was taken as the viscosity value. The sample was loaded onto the instrument plate, the rotor gap was set to 250 μm, and the kinematic viscosity was measured while increasing the shear rate from 1 (1 / s) to 10000 (1 / s).

[0105] 2) Thickness

[0106] Ten layers of the composite membrane were stacked, and their thickness was measured using a Mitutoyo ID-C112X at room temperature and pressure to obtain the average thickness of the 10 composite membrane layers. The average thickness of the 10 composite membrane layers was then divided by 10 to obtain the thickness of the composite membrane. The thickness of the porous substrate (9 μm) was subtracted from the thickness of the composite membrane to obtain the total thickness of the ceramic layer.

[0107] 3) Adhesive force

[0108] [Cardboard Test]

[0109] The composite diaphragm was cut into 5cm × 10cm samples for preparation. A 2cm × 10cm black cardboard and a rubber pad were placed sequentially on the ceramic layer of the composite diaphragm sample. With a force of 10N applied to the rubber pad using a pressing device, the cardboard was pulled horizontally 60mm at a speed of 0.1m / s. The adhesive force was evaluated based on the degree to which foreign matter adhered to the cardboard surface. The foreign matter could be a component of the ceramic layer, such as inorganic particles, adhesive, or a combination thereof.

[0110] [Evaluation of the degree of foreign body adhesion]

[0111] After the cardboard test, the cardboard surface was photographed and imaged using an optical camera, and the area of ​​adhered foreign matter was measured. Specifically, indirect lighting was set up by setting the LED lamps in the visible light area at a 60° angle, and a 640MP optical camera was used to photograph the cardboard at a height of 40cm from the sample (cardboard). The captured cardboard images were imported into ImageJ, and then the cropping function was used to select and crop only the area passing through the diaphragm and rubber pad. The image file of the cropped area was then converted to an 8-bit image, and a sharpening filter was applied to the image to adjust the brightness and contrast for easy differentiation between the cardboard and the white foreign matter. A threshold was applied to the image and it was converted to a binary image. The Analyze Particles function was used to calculate the ratio of the area occupied by the white foreign matter to the total area, and the adhesive strength was evaluated according to the following benchmarks.

[0112] A: <1.5%

[0113] B: 1.5% to 5%

[0114] C: >5%

[0115] 4) Thermal shrinkage rate

[0116] The heat shrinkage rate of the composite diaphragm was measured based on ASTM D1204 standard using the following method: On the composite diaphragm sample, grid points were marked at 2cm intervals on a 10cm square. One side of the square was for the transverse direction (TD), and the other side for the machine direction (MD). The sample was placed in the center, with five sheets of paper placed above and below it. The four sides of the paper were wrapped with tape. The paper-wrapped sample was then placed in a hot air drying oven at 150°C for 60 minutes. Afterward, the sample was removed, and the diaphragm was observed with a camera. The machine direction (MD) shrinkage rate and the transverse direction (TD) shrinkage rate were calculated and recorded in Table 1 below.

[0117] MD heat shrinkage rate (%) = (MD length before heating - MD length after heating) / MD length before heating × 100

[0118] TD heat shrinkage rate (%) = (TD length before heating - TD length after heating) / TD length before heating × 100

[0119] [Example 1]

[0120] Boehmite with an average particle size (D50) of 0.3 μm and dispersant 1,2-benzisothiazolin-3-one (DIO2) were mixed in water, wherein the dispersant was 2 parts by weight relative to 100 parts by weight of the boehmite, thereby obtaining a slurry with a solid content of 45% by weight. The obtained slurry was mixed with a binder, wherein the weight ratio of carboxymethyl cellulose (CMC) with a degree of substitution of 0.9 and a weight average molecular weight of 200,000 g / mol to polyacrylamide (PAAm) (Mw of 200,000 g / mol, Sigma-Aldrich) in the binder was 10:90, and 3 parts by weight of binder (CMC:PAAm = 10:90 weight ratio) were mixed relative to 100 parts by weight of the boehmite, and diluted with water to a total solid content of 25% by weight, thereby obtaining a composition for ceramic layer formation.

[0121] Corona discharge treatment (power density 2 W / m²) was applied to both sides of a 9 μm thick polyethylene film (porosity 35% to 45%, SKIET). 2 To introduce surface polar groups, the corona surface treatment speed is set to 5 meters per minute (mpm). The ceramic layer forming composition is coated onto both sides of the corona-treated polyethylene film by bar coating and dried at 50°C to obtain a composite diaphragm with ceramic layers of the same thickness on both sides.

[0122] [Example 2]

[0123] The same method as in Example 1 was used, except that CMC with a degree of substitution of 0.8 and a weight-average molecular weight of 250,000 g / mol was used, and the mixing ratio of CMC to PAAm was changed to a weight ratio of 40:60.

[0124] [Example 3]

[0125] The procedure was carried out using the same method as in Example 1, except that CMC with a degree of substitution of 1.0 and a weight-average molecular weight of 300,000 g / mol was used.

[0126] [Example 4]

[0127] The procedure was carried out using the same method as in Example 1, except that CMC with a degree of substitution of 0.9 and a weight-average molecular weight of 500,000 g / mol was used.

[0128] [Example 5]

[0129] The procedure was carried out using the same method as in Example 1, except that CMC with a degree of substitution of 0.9 and a weight-average molecular weight of 1,000,000 g / mol was used.

[0130] [Comparative Example 1]

[0131] The same method as in Example 1 was used, except that the mixing ratio of CMC to PAAm was changed to a weight ratio of 50:50.

[0132] [Comparative Example 2]

[0133] The process is carried out using the same method as in Example 1, except that PAAm is used alone as the adhesive.

[0134] [Comparative Example 3]

[0135] The procedure was carried out using the same method as in Example 1, except that CMC with a degree of substitution of 0.9 and a weight-average molecular weight of 150,000 g / mol was used.

[0136] [Comparative Example 4]

[0137] The procedure was carried out using the same method as in Example 1, except that CMC with a degree of substitution of 0.5 and a weight-average molecular weight of 250,000 g / mol was used.

[0138] [Comparative Example 5]

[0139] The procedure was carried out using the same method as in Example 1, except that CMC with a degree of substitution of 1.3 and a weight-average molecular weight of 250,000 g / mol was used.

[0140] [Table 1]

[0141]

[0142] Referring to Table 1, it can be seen that the composite separator according to one embodiment of the present invention uses a binder comprising carboxymethyl cellulose and polyacrylamide in a specific mixing ratio (10 to 40:90 to 60 by weight) while satisfying a weight-average molecular weight of 180,000 g / mol or higher and a degree of substitution of 0.6 to 1.2. Therefore, not only is there excellent adhesion between the substrate and the ceramic layer interface, but also excellent adhesion between the inorganic particles within the ceramic layer, and thermal shrinkage can be effectively suppressed. Furthermore, electrochemical devices using the composite separator according to one embodiment can ensure heat resistance and safety, and can facilitate high capacity and high power output.

[0143] On the other hand, it was confirmed that in the composite membranes of Comparative Examples 1 to 5, which used CMC that was not within the range of the above-mentioned weight-average molecular weight and / or degree of substitution or that was not within the range of the above-mentioned mixing ratio of CMC and PAAm, the heat resistance of the ceramic layer deteriorated significantly, and therefore the thermal shrinkage rate increased significantly, and the adhesion also decreased.

[0144] The composite separator of this invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, the separator of this invention can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0145] As described above, the present invention has been illustrated with specific content and limited embodiments, but this is only provided to help to understand the present invention more fully. The present invention is not limited to the above embodiments, and those skilled in the art can make various modifications and variations based on these descriptions.

[0146] Therefore, the present invention should not be limited to the embodiments described above, and all contents that are equivalent to or have equivalent variations of the claims fall within the scope of the present invention.

Claims

1. A composite separator, the composite separator comprising: Porous substrate; And a ceramic layer formed on one or both sides of the porous substrate, the ceramic layer comprising inorganic particles and a binder. The adhesive comprises polyacrylamide in a weight ratio of 60 to 90:40 to 10 and carboxymethyl cellulose having a weight-average molecular weight of more than 180,000 g / mol and a degree of substitution of 0.6 to 1.

2.

2. The composite diaphragm according to claim 1, wherein, The carboxymethyl cellulose has a weight-average molecular weight of 180,000 g / mol to 1,500,000 g / mol.

3. The composite diaphragm according to claim 1, wherein, The degree of substitution of the carboxymethyl cellulose is 0.7 to 1.

0.

4. The composite diaphragm according to claim 1, wherein, The polyacrylamide has a weight-average molecular weight of 150,000 g / mol to 250,000 g / mol.

5. The composite diaphragm according to claim 1, wherein, The content of the adhesive is from 0.1 parts by weight to 10 parts by weight relative to 100 parts by weight of the inorganic particles.

6. The composite diaphragm according to claim 1, wherein, The inorganic particles have an average particle size of 0.1 μm to 1.0 μm.

7. The composite diaphragm according to claim 1, wherein, The inorganic particles are selected from one or more of boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3 and SiC.

8. The composite diaphragm according to claim 1, wherein, The porous substrate has undergone hydrophilic surface treatment.

9. The composite diaphragm according to claim 1, wherein, The total thickness of the ceramic layer is 0.5 μm to 10 μm.

10. The composite diaphragm according to claim 1, wherein, The mechanical and transverse thermal shrinkage rates of the composite diaphragm were both less than 4% after being placed at 150°C for 60 minutes.

11. The composite diaphragm according to claim 1, wherein, When evaluating the degree of foreign matter adhesion to the paperboard surface after conducting paperboard tests on the composite diaphragm, the area occupied by the adhered foreign matter relative to the paperboard area was less than 5%. In the paperboard test, a black paperboard measuring 2cm × 10cm and a rubber pad were placed sequentially on the ceramic layer of a composite diaphragm sample measuring 5cm × 10cm. With a force of 10N applied to the rubber pad using a pressing device, the paperboard was pulled out horizontally at a speed of 0.1m / s to test the degree to which foreign matter adhered to the surface of the paperboard.

12. A method for manufacturing a composite diaphragm, comprising the steps of coating a ceramic layer forming composition containing a binder and inorganic particles onto one or both sides of a porous substrate and drying to form a ceramic layer, in, The adhesive comprises polyacrylamide in a weight ratio of 60 to 90:40 to 10 and carboxymethyl cellulose having a weight-average molecular weight of more than 180,000 g / mol and a degree of substitution of 0.6 to 1.

2.

13. An electrochemical device, said electrochemical device comprising a positive electrode, a negative electrode, and a composite separator, in, The composite membrane comprises: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, wherein the ceramic layer comprises inorganic particles and a binder. The adhesive comprises polyacrylamide in a weight ratio of 60 to 90:40 to 10 and carboxymethyl cellulose having a weight-average molecular weight of more than 180,000 g / mol and a degree of substitution of 0.6 to 1.2.

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